1. Field of the Invention
This invention relates to observing or illuminating optical fiber bundles for endoscopes. More particularly, it relates to an endoscope optical fiber bundle which is made both suitably flexible and rigid to improve its durability.
2. Background of the Invention
In general, an endoscope optical fiber bundle is covered by a flexible cover tube. If the inside diameter of the cover tube is relatively close to the outside diameter of the optical fiber bundle, the assembly of the optical fiber bundle and the cover tube is so stiff, resembling a bar, that the optical fibers are liable to be broken when bent.
Therefore, heretofore, the optical fiber bundle is so designed that the sectional area s of the optical fibers bundled tight is about half (1/2) of the sectional area S of the hollow of the cover tube which is made circular in section i.e. s=0.50S.
As was described above, the conventional endoscope optical fiber bundle is loosely inserted into the cover tube to the extent that the relation s=0.50S is established. Therefore, the assembly of the optical fiber bundle and the cover tube can be readily and smoothly bent. However if, when a flexible tube a of an endoscope or a bending part b connected to the flexible tube a is bent with a small radius of curvature as shown in FIG. 4, an optical fiber bundle c is on the inner edge of the curve. It is then possible that the optical fiber bundle c is bent in a zigzag and is buckled. Therefore, if this operation is repeatedly carried out, the fibers are broken, thus obstructing the observation or illumination.